Field
The present disclosure relates generally to devices and methods that provide improved correction of various refractive errors by providing both central corneal reshaping as well as mid-peripheral corneal refractive effects to regulate refractive error development in an eye.
Discussion of the Related Art
The use of contact lenses for correction of refractive errors of the eye such as myopia, hyperopia, and astigmatism generally relies on one of two approaches. The first approach is a conventional refractive correction to adjust the focal length of the eye in order to place the focused image on the fovea. This adjustment is accomplished by placing a contact lens having a predetermined refractive power in the light path. A second approach is application of a contact lens to reshape the cornea's surface geometry such that the reshaped cornea's refractive power brings the image into proper focus on the fovea. This second method is generally referred to as corneal refractive therapy, corneal reshaping or orthokeratology.
Refractive error correction using corneal reshaping contact lenses is attractive because the reshaping lenses are worn for relatively short periods of time, such as during sleep, when the wearer is inactive. Refractive error correction via corneal reshaping may be safer and more desirable than complete reliance on corrective contact lenses during the daytime or other periods of active use of vision. Modern overnight corneal reshaping lenses have been successfully used to temporarily correct refractive errors such as myopia, hyperopia, and astigmatism.
However, the corrective effect achieved by reshaping is not permanent, and the reshaping lenses must be worn regularly by a user for the corrected corneal shape to be maintained.
While various approaches to refractive error correction may provide focused vision, structural changes to an eye may lead to progressive development of further refractive error in spite of the corrective measures taken. The importance of a relationship between refraction of a mid-peripheral portion of the cornea and the focal distance produced with respect to the peripheral retina on the progression of various refractive errors has been recognized. For example, a hyperopic defocus at the peripheral retina has been found to influence progression of myopia by stimulating axial elongation of the eye. Recognizing this effect, some lens designers have produced contact lenses for daytime use with central myopic corrective zones (focusing axial light on the fovea) and mid-peripheral refractive zones that produce myopic peripheral retinal defocus. These lenses produce modest regulation of myopic progression, but require continuous daytime use for refractive error correction. Hence, the usefulness of these corrective lenses in regulating myopic progression is only derived during daytime wear, and they do not provide the benefit of corneal reshaping. On the other hand, overnight wear corneal reshaping lenses used for correction of myopia provide no benefit similar to that described above when worn for open-eye daytime activity with respect to regulation of myopic progression. Indeed, such lenses may induce an undesirable hyperopic defocus during daytime wear that can produce an effect opposite of that required for regulation of myopic progression.
There is thus a need in the art for multifunction therapeutic optical devices that can provide both correction of refractive error by achieving desired corneal reshaping as well as regulation of refractive error development by producing a predetermined peripheral retinal focus or defocus.